Shred the cooked chicken breasts.
Poach two chicken breasts in chicken stock before shredding, or use pre-cooked rotisserie chicken if preferred.
Lightly crush the lemongrass with the back of a knife to release its flavor for the soup.
Heat a large pot over medium heat, adding butter and oil.
Sauté the mushrooms and red pepper for a few minutes.
Stir in the ginger and garlic, cooking briefly for about 20 seconds.
Add curry paste and toast it for about 10 seconds.
Deglaze the pot with chicken stock, incorporating the poaching stock if available, and stir in coconut milk, shredded chicken, lime juice, lime zest, fish sauce, lemongrass, and scallions.
Let the soup simmer uncovered for 15 minutes to develop its flavors.
Add the zucchini and cook for another 15 minutes until tender.
Remove the lemongrass from the soup before serving.
Garnish with fresh cilantro and a squeeze of lime for added freshness.
Store leftovers in the fridge for a few days or freeze for longer storage.